The invention relates to ski bindings in general, and more particularly to improvements in safety ski bindings which automatically release the boot in response to the application of forces whose magnitude warrants separation of the boot from the ski in order to prevent or at least reduce the likelihood of injury to the skier.
German Auslegeschrift No. 1,201,738 discloses a safety ski binding wherein a sheet metal plate is reciprocable in arcuate guides in directions substantially transversely of the skiing direction. That portion of the sole of a ski boot which is located immediately below the ball behind the toes of the skier's foot rests directly on the plate and the center of curvature of the arcuate path defined by the guides is located below the heel of the boot. The plate rests on and is slidable relative to a sheet metal base whose upper side has friction-reducing ribs engaging the underside of the plate. The tip of the boot is urged against a pivotable jaw of the binding by a cable, and the jaw has a hold-down device for the front portion of the boot. A reciprocable tongue is employed to separably couple the plate to the jaw; the jaw has a pin which extends into a slot of the tongue when the plate assumes its operative position. Each movement of the plate from its operative position must be preceded by a pivotal movement of the jaw from an operative position in which the hold-down device engages the boot. Such movement of the jaw results in withdrawal of the pin from the slot of the tongue and thus frees the plate for movement along the arcuate path. The plate has upwardly extending flanges which are engaged by the respective sides of the sole resting on the plate and insure that the plate shares lateral movements of the sole upon movement of the jaw from its operative position.
The patented binding exhibits a number of serious drawbacks. First of all, the boot is shifted relative to the hold-down device during disengagement of the plate from the base, i.e., the boot acts not unlike a component part of the binding which means that the facility with which the plate is disengaged from the base depends on the material and/or configuration of the boot. Secondly, the aforementioned ribs merely reduce friction between the plate and the base, i.e., friction between the plate and the arcuate guides is quite pronounced so that the magnitude of the force which must be applied in order to disengage the plate from the base cannot be selected with a satisfactory degree of reproducibility. As a rule, the front and rear edge portions of the plate are received in dovetailed guides whose resistance to sliding movement of the respective edge portions is rather high. Frictional engagement between the guides and the edge portions of the plate is even more pronounced if one of the hold-down devices (normally the rear hold-down device) embodies or is combined with springs which urge the boot against the other hold-down device, i.e., in or counter to the skiing direction. Still further, the patented binding is not suited for cross country skiing because, were such binding mounted on the front portion of a cross country frame whose front end is pivoted to the ski, the aforementioned jaw would prevent the placing of the tip of the sole of a ski boot in line with the pivot of the frame so that a cross country skier would be compelled to lift the rear portion of the ski off the ground in response to each lifting of the heel of the boot.
German Offenlegungsschrift No. 2,157,791 discloses a ski binding wherein the entire underside of the boot rests on a plate cooperating with a release mechanism which allows the plate and the boot to become disengaged from the ski in the event of an accident or whenever the boot and/or the plate is subjected to the action of large forces acting transversely of the skiing direction and in parallelism with the upper side of the ski. A drawback of such bindings is that their weight greatly exceeds the maximum acceptable or recommended weight, especially for cross country skiing. Also, if the plate is very rigid, it unduly increases the stiffness of the adjacent portion of the ski. On the other hand, a flexible plate is likely to undergo excessive deformation in response to flexing of the ski so that the plate will be incapable of adequately supporting or will become disengaged from the boot in situations and under circumstances when such disengagement is not only undesirable but also dangerous. Known proposals to avoid excessive stiffening of the ski or undersirable deformation of the plate contribute significantly to the initial cost and bulk of the just discussed binding.